electronics house) connected as shown:
>>
>> Gnd----[220ohm]---+---[220ohm]----+5
>>                   |
>>                   +---[LED]------- Port pin
>>

This can also be used with separate red and green LEDs in inverse parallel,
e.g. a panel display to indicate TOO HIGH (red LED); TOO LOW (green LED);
or within range (tri-stated to open circuit - no LEDs).


> Port pin---+-[220ohm]--+---[LED]------  Port pin
>            |
>            +-[220ohm]--+---[LED]------- Port pin
>            |
>            +-[220ohm]--+---[LED]------- Port pin
>            |
>            +-[220ohm]--+---[LED]------- Port pin
>

>The question that popped into my mind during this design discussion was
>the relevance of the position of the resistor. Does it matter if the resistor
>is on the anode or the cathode side of an LED. Is putting the resistor on
>the anode side simply a convention or is there some other reason that justifies
>its placement. Should a bi-polar have resistance on both sides (I've done this
>in previous designs)?
>

In a series circuit, the same current flows through all elements, so it
makes no difference which side the resistor is on. Also, if you only need
to light one of the LEDs at a time, you can simplify this by using a single
resistor at the port pin.

.....................Reg Neale.....................
"Ignorance is a renewable resource"   P.J. O'Rourke